1. Field of the Invention
The present invention relates generally to a giant magnetoresistance device, and more particularly, to a current perpendicular-to-the-plane magnetoresistance (CPP-MR) head for reading magnetic signals from a magnetic medium.
2. Description of the Related Art
Giant magnetoresistance (GMR) was first described by Baibich et al. [Phys. Rev. Lett. 61, 2472 (1988)]. The discovery of GMR triggered numerous studies on the transport properties of magnetic multilayers. In most cases, the current flows in the plane of the layers and is known as current-in-the-plane magnetoresistance (CIP-MR).
Pratt et al. extended the GMR studies to the case where the current flows perpendicular to the plane, thereby causing current-perpendicular-to-the-plane magnetoresistance (CPP-MR). [See, for example, Phys. Rev. Lett. 66, 3060 (1991).] In general, signals caused by CPP-MR are several times larger than those caused by CIP-MR.
The physical origin for both CIP-MR and CPP-MR is that the application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This variation causes a change in the spin-dependent scattering of conduction electrons and, therefore, the electrical resistance of the structure. In a multi-layer structure having a configuration of [ferromagnetic/nonmagnetic]n, the GMR amplitude oscillates with variations in the nonmagnetic layer thickness due to the oscillation of coupling between neighboring ferromagnetic layers that orients the magnetizations of neighboring ferromagnetic layers antiparallel or parallel. In general, the oscillation period is about 12 angstromsxe2x80x94slightly depending on the nonmagnetic material. Thus, fluctuation and uniformity of the nonmagnetic layer thickness cause a dispersion of the coupling between the neighboring ferromagnetic layers. However, the antiparallel configuration, for example, between the magnetizations of neighboring ferromagnetic layers are not perfect, thereby reducing the GMR amplitude from the ideal situation.
The reduction in GMR amplitude may be minimized or eliminated using a spin valve structure as described by B. Dieny et al. in Phys. Rev. B43, 1297 (1991). A standard spin valve comprises two ferromagnetic layers separated by a nonmagnetic spacer such as Cu. The magnetization of one ferromagnetic layer is fixed by an adjacent antiferromagnetic layer or permanent magnetic layer, thereby preventing rotation in the presence of the field of interest. As a result, there is only one possible orientation for the magnetization of this ferromagnetic layer. The magnetization of the other ferromagnetic layer is not fixed and can freely rotate in the presence of an external field.
U.S. Pat. No. 5,668,688 to Dykes et al. (which is hereby incorporated by reference) describes a CPP spin valve type magnetoresistance transducer. However, for ultra high areal density (i.e., over 100 Gbit per square inch) applications, there are at least two limitations that result from the arrangement disclosed in Dykes et al. First, the read gap in that arrangement is limited by the spin valve thickness. Second, due to the current perpendicular-to-the-plane model, the magnetoresistance of this spin valve structure is insufficient for ultrahigh areal density applications.
Accordingly, the present invention is directed to a current perpendicular-to-the-plane magnetoresistance head that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a magnetoresistance device having a small read gap.
Another object of the present invention is to provide a magnetoresistance device having a read gap that is not limited by a spin valve thickness.
Another object of the present invention is to provide a magnetoresistance device that achieves an ultrahigh areal density.
Another object of the present invention is to provide a magnetoresistance device having a high output.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a current perpendicular-to-the-plane magnetoresistance (CPP-MR) device includes a first magnetic shield formed of an electrically conductive and magnetically shielding material; a second magnetic shield formed of an electrically conductive and magnetically shielding material, the first and the second magnetic shield disposed to define a read gap therebetween; and a spin valve structure disposed between the first and second magnetic shields, the spin valve structure being electrically connected and magnetically separated from the first and second magnetic shields such that the first and second magnetic shields act as electrical contact leads.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.